The present invention relates to a direct current motor provided with a plurality of armature windings disposed around a disc-shaped or cylindrical coreless armature.
Conventionally, a number of motors of the type with an armature core having a plurality of armature windings formed in a lap winding or wave winding manner are widely used. However, when the conventional armature windings are employed in the coreless type motor, various shortcomings are encountered as will be explained by referring to FIGS. 1 and 2. FIGS. 1 and 2 are expanded views of armature windings in the case where conventional armature winding formed in a wave winding manner are employed in a coreless motor. More specifically, FIG. 1 is an expanded view of a wave winding armature comprising five armature coils, provided with a field magnet with six magnetic poles. The filed magnet 1 has magnetic poles 1-1, 1-2, . . . , and 1-6, magnetized alternately to N and S with 60 degree angular intervals. A commutator 3 comprises commutator segments 3-1, 3-2, 3-3, 3-4, and 3-5, with 72 degree angular intervals (6/5 the magnetic pole width). An armature 2 is a cross-connected normal winding, with the angular intervals of the electrically conductor portion contributing to the generation of torque in each armature coil set equal to the magnetic pole width. Armature coils 2-1, 2-2, 2-3, 2-4 and 2-5 are each disposed with an equal pitch of an angular interval of 72 degrees (6/5 the magnetic pole width), without being superimposed on each other. Each armature coil is subjected to wave winding connection. The connecting portions of the armature coils 2-1 and 2-3, the armature coils 2-3 and 2-5, of the armature coils 2-5 and 2-2, of the armature coils 2-2 and 2-4, and of the armature coils 2-4 and 2-1 are respectively connected to commutator segments 3-2, 3-4, 3-1, 3-3 and 3-5. To brushes 4-1 and 4-2 is supplied power from D.C. power source positive and negative poles 5-1 and 5-2, respectively. The brushes 4-1 and 4-2 are disposed with 180 degree angular intervals (3/1 the magnetic pole width). In the configuration as shown in FIG. 1, electric current flows in the direction of the arrow, and torque is generated in each armature coil, so that the armature 2 and the commutator 3 are respectively rotated in the directions of the arrows A and B and work as commutator motor. In the example as shown in FIG. 1, the number of the armature coils is so small that the switching of armature current is performed 10 times per revolution (except the singular point) and therefore good commutating characteristics cannot be obtained. Due to the poor commutating characteristics, reverse torque is generated and the operation efficiency and the starting torque are reduced. Furthermore, since the number of armature coils present between the positive pole and the negative poles of the D.C. power source is extremely small, this cannot be used as direct current motor for high voltage. Furthermore, sparking frequently takes place and short-circuit troubles are apt to occur. As a result, the life of the motor is shortened. In order to improve on the above-mentioned shortcomings, it has been proposed to construct the armature coils in multiple layers. Referring to FIG. 2, this will now be explained. FIG. 2 is an expanded view of a wave winding armature comprising 15 armature coils, provided with a field magnet with six magnetic poles. The field magnet 1 is exactly the same as that explained in FIG. 1. A commutator 7 comprises commutator segments 7-1, 7-2, . . . , 7-15, with 24 degree angular intervals (2/5 the magnetic pole width). An armature 6 is constructed of a cross-connected normal triple-superimposed wave winding coil, in which the angular intervals of the conductor portions thereof contributing to the generation of torque in each armature coil are equal to the magnetic pole width. The armature coils 6-1, 6-2, . . . , 6-15 are arranged, superimposing on each other, in multiple layers, with an equal pitch of 24-degree angular intervals (2/5 the magnetic pole width). Each armature coil is subjected to wave winding connection. The respective connecting portions of the armature coils 6-1 and 6-7, of the armature coils 6-7 and 6-13, of the armature coils 6-13 and 6-4, of the armature coils 6-4 and 6-10, and of the armature coils 6-10 and 6-1 are connected to commutator segments 7-4, 7-10, 7-1, 7-7 and 7-13. The respective connecting portions of the armature coils 6-2 and 6-8, of the armature coils 6-8 and 6-14, of the armature coils 6-14 and 6-5, of the armature coils 6-5 and 6-11, and of the armature coils 6-11 and 6-2 are connected to commutator segments 7-5, 7-11, 7-2, 7-8 and 7-14. The respective connecting portions of the armature coils 6-3 and 6-9, of the armature coils 6-9 and 6-15, of the armature coils 6-15 and 6-6, of the armature coils 6-6 and 6-12, and of the armature coils 6-12 and 6-3 are connected to commutator segments 7-6, 7-12, 7-3, 7-9 and 7-15. As mentioned previously, since the armature 6 is of the cross-connected normal triple wave winding type, there are disposed three pairs of brushes. A positive pole 5-1 and a negative pole 5-2 of DC power source respectively supply power to the brushes 4-1 and 4-2. A positive pole 5-3 and a negative pole 5-4 of DC power source respectively supply power to the brushes 4-3 and 4-4. A positive pole 5-5 and a negative pole 5-6 of DC power source respectively supply power to the brushes 4-5 and 4-6. The angular intervals of those brushes are 60 degrees (the magnetic pole width). In the configuration shown in FIG. 2, electric current flows in the direction of the arrow and torque is generated in each armature coil, so that the armature 6 and the commutator 7 respectively rotate in the directions of the arrows A and B and constitute a commutator motor. In the commutator motor shown in FIG. 2, the armature coils are superimposed in multiple layers and, therefore, the armature is thick. That thickness of the armature significantly reduces the effective magnetic field of the field magnet which passes through the armature. As a result, the motor efficiency and starting torque are decreased. In order to eliminate those shortcomings, the prior art effort has been directed to decreasing the thickness of the conductor portions contributing to the generation of torque. However, this process for decreasing the thickness of the conductor portions is performed by press molding, and accordingly is often accompanied by such defects as breaking and short-circuiting of the armature coils. Further, since the phase relationship between the armature coils cannot be positively held in the desired state at the time the coils are arranged, correct phase relationship between the windings is liable to be distorted. Accordingly, such prior art DC motors are costly and cannot be mass produced.
Another prior art technique used for conventional cylindrical coreless DC motors, for avoiding superimposition of the opposite edge portions of the armature coils on each other, requires that the insulated wire be wound in alignment, turn by turn, alternately at an angle of about 180 degrees, so that a cylindrical armature is formed, with the entire width of winding, or part thereof slanting with respect to the rotating axis. This technique, however, also is costly and cannot be used for mass-production.
Further, in Japanese Patent Publication Sho 44-4450, there is disclosed a DC motor having armature coils with .+-.1 magnetic pole for a field magnet with 4 or more magnetic poles, and commutator segments, the number of which is two times the number of the armature coils.
In the case where a field magnet with 4 magnetic poles is employed, the motor efficiency and the starting torque are high. However, in the case where a field magnet with 6 or more magnetic poles is employed and the number of commutator segments is two times the number of the armature coils, reverse torque is generated and, accordingly, the motor efficiency and the starting torque are significantly decreased.